When evaluating the performance of optical transport networks, it is often necessary to monitor the bit-error rate (“BER”) and its implications on offering a given network service. The BER is the number of bit errors occurring within a specified time interval. For example, BER can be expressed by the equation:BER=N/T,where N is the number of bit errors and T is the time interval.
In practice, however, there are no universally agreed-upon values for the parameters, N and T. Different network test platforms may monitor the BER using different values, which makes it difficult to consistently monitor the BER. To make reliable measurements of system performance (such as protection switching times), it is necessary for the test platforms to be flexible enough so that they can monitor the BER over a wide range of values of N and T. Presently, no test platforms incorporate the flexibility to monitor the BER over a wide range of values for N and T.
When evaluating the suitability of a platform for a given application (such as video transport, or other data transport applications) it might be necessary to generate a BER with a given combination of values for N and T. The distribution of total bit errors N over the extent of period T, is referred to as the BER profile. The ability to generate a specific BER profile is especially critical for systems that employ forward error correction (“FEC”). All FEC techniques have limitations in the maximum number of contiguous bit errors they can correct. For example, suppose a particular FEC algorithm is known to operate reliably under a BER of 10−6 (1 error in 1 million bits). Given two profiles with the same number of bit errors over the same time interval, the FEC algorithm may be perfectly capable of correcting bit errors for one BER profile, but not another profile. FIGS. 1 and 2 illustrate two different BER profiles with the same total number of bit errors (N) over the same time interval (T) but with different error distributions over the time interval. A particular FEC algorithm may be able to correct errors for the profile shown in FIG. 1, but may not be able to correct the errors for the BER profile shown in FIG. 2. This is a substantial problem for downstream end-customers. For example, in the case of video transmission, an uncorrectable, rapid burst of a relatively small number of errors would result in video quality degradations such as tiling.